fix: handle installer errors and avoid Arch partial upgrades

Install Arch dependencies using the existing package database and explain how to recover from stale package metadata. Avoid errexit on the first firmware count, handle Secure Boot prompt EOF as cancellation, propagate error traps into functions, and reject empty firmware sources before modifying installed firmware.

Validation: eight isolated installer regression tests pass; the original installer fails the affected cases. Bash syntax and ShellCheck error-level checks pass. Fixes #100. Addresses the confirmed findings in #108; other audit suggestions remain separate.

install.sh

@@ -9,7 +9,7 @@
 # FIX: Corrected DKMS module configuration for aic8800_fdrv
 #############################################################################
 
-set -e  # Exit on error
+set -eE  # Exit on error and run the ERR trap inside functions
 
 # Color definitions
 readonly RED='\033[0;31m'
@@ -152,7 +152,8 @@ check_secure_boot() {
         echo "  2. Sign the module manually (advanced)"
         echo "  3. Continue installation anyway (module may fail to load)"
         echo ""
-        read -p "Continue installation? (y/N): " choice
+        local choice
+        read -r -p "Continue installation? (y/N): " choice || choice="n"
         if [[ ! "$choice" =~ ^[Yy]$ ]]; then
             print_info "Installation cancelled by user."
             exit 0
@@ -268,15 +269,15 @@ install_dependencies() {
             ;;
             
         pacman)
-            print_info "Syncing package database..."
-            run_logged "Package database sync" pacman -Sy --noconfirm
-
             local -a packages=(dkms base-devel mokutil util-linux usb_modeswitch)
             if [ "$install_kernel_headers" = true ]; then
                 packages+=(linux-headers)
             fi
             print_info "Installing: ${packages[*]}..."
-            run_logged "Dependency installation" pacman -S --needed --noconfirm "${packages[@]}"
+            if ! run_logged "Dependency installation" pacman -S --needed --noconfirm "${packages[@]}"; then
+                print_error "Check the pacman errors above. If the package database is stale, run 'sudo pacman -Syu', reboot if the kernel was updated, then rerun this installer."
+                return 1
+            fi
             ;;
             
         zypper)
@@ -390,6 +391,22 @@ install_firmware() {
         exit 1
     fi
 
+    # Validate the source before changing any installed firmware or config.
+    local -a fw_dirs=()
+    local fw_dir
+    for fw_dir in "$fw_base"/aic8800*; do
+        [ -d "$fw_dir" ] || continue
+        if [ -z "$(find "$fw_dir" -type f -name '*.bin' -print -quit)" ]; then
+            print_error "No firmware binaries found in $fw_dir; existing firmware has not been changed."
+            exit 1
+        fi
+        fw_dirs+=("$fw_dir")
+    done
+    if [ "${#fw_dirs[@]}" -eq 0 ]; then
+        print_error "No firmware directories found in $fw_base; existing firmware has not been changed."
+        exit 1
+    fi
+
     cleanup_legacy_bluetooth_config
 
     # Remove old firmware versions
@@ -400,7 +417,7 @@ install_firmware() {
 
     # Copy all firmware variants
     print_info "Installing firmware for all chip variants..."
-    for fw_dir in "$fw_base"/aic8800*; do
+    for fw_dir in "${fw_dirs[@]}"; do
         if [ -d "$fw_dir" ]; then
             local fw_name=$(basename "$fw_dir")
             local fw_dest="/lib/firmware/$fw_name"
@@ -713,7 +730,7 @@ verify_installation() {
     local fw_count=0
     for fw_dir in /lib/firmware/aic8800*; do
         if [ -d "$fw_dir" ]; then
-            ((fw_count++))
+            fw_count=$((fw_count + 1))
         fi
     done
     if [ $fw_count -gt 0 ]; then